Wind-turbines are conventionally mounted on top of steel-towers. The towers consist usually of a number of modules.
As the price of steel is increasing more than the price of concrete it is advantageous to build wind-turbine-towers of concrete.
For large experimental wind-turbines it is known to build and use concrete towers, which are built by using a so called “slip-form pouring method”. One example of this kind of tower was built 1977 for the Tvind-turbine in Denmark.
This method has the disadvantage that the concrete has to be filled into a mould, which is located at the top of the tower. At the end of the construction procedure the concrete has to be filled into the mould at the final height of the tower. In dependency of this height the efforts for the fill-in increases. Furthermore personnel are required to fill-in in the concrete into the mould at this final-height, so their work is limited by the time of the day, by health-regulations and by safety-requirements due to the height.
The WO 07025947 A1 discloses a method whereby a concrete tower is extruded vertically. This method has the disadvantage that it requires a very substantial technical arrangement, since high pressure is required for large-dimension components in order to push up the tower during casting. Large pressures at large diameters require very large technical arrangements.
It is also known to build concrete towers by the use of pre-casted segments. Such segments show dimensions which might anticipate the transport of the segments via roads or bridges. So additional effort need to be done to solve the problems of transportation.
It is known to build concrete towers by stacking of complete cylindrical elements. These elements are connected together by a number of post-tension cables. After the stacking of the elements a number of post-tension cables are inserted into channels in the tower walls. The channels transit the tower from the top to its bottom, while each post-tension cable is without discontinuation so the cable might reach a great effective length in dependency to the tower height. After cable insertion the channels are filled with a slurry material.
This arrangement has the disadvantage that for a high tower a reliable injection of the slurry needs special precautions.
Furthermore it may be difficult to insert the cables in the channels, particularly for a high tower.
The U.S. Pat. No. 7,114,295 discloses an improved method to solve these problems. A funnel-shaped apparatus is used for guiding the tension-cables and for establishing a seal to produce a pressure-tight transition between two tower segments. However despite these arrangements the problem remains to insert the post-tension-cables and to inject slurry into the channel for greater tower heights.
The U.S. Pat. No. 7,106,085 discloses a tower consisting of segments where no post-tension-cables are needed. This arrangement has the disadvantage that numerous mounting operations are required and that a high number of fasteners are needed.
The US 2008 004 0983 A1 discloses a tower consisting of segments. The segments do not require tensioning-cables, because they are pre-assembled on ground. This arrangement has the disadvantage that numerous mounting operations are required and that a high number of fasteners are needed.
The WO 08031912 A1 discloses a wind-turbine-tower, which is mounted with pre-fabricated elements. The tower has longitudinal ribs, which form longitudinal joints. These joints comprise metal elements and high resistance mortar. This leads to the disadvantage that numerous mounting operations are required and that a high number of fasteners are needed. Additionally high-strength mortar is needed.